Automated upper/lower head cross direction alignment based on measurement of sensor sensitivity

Abstract

A method includes moving a first sensor assembly to a plurality of cross direction positions relative to a second sensor assembly, where the first and second sensor assemblies are configured to move in the cross direction relative to a web of material. The method also includes, for each of the plurality of cross direction positions, determining a sensor value associated with a sensor source disposed at the second sensor assembly as measured by a sensor receiver disposed at the first sensor assembly. The method further includes determining a starting alignment position of the first sensor assembly to be a first cross direction position where a difference between the sensor value at the first cross direction position and a corresponding sensor value at one or more adjacent cross direction positions is a minimum.

What is claimed is: 
     
         1 . A method comprising:
 moving a first sensor assembly to a plurality of cross direction positions relative to a second sensor assembly, the first and second sensor assemblies configured to move in the cross direction relative to a web of material;   for each of the plurality of cross direction positions, determining a sensor value associated with a sensor source disposed at the second sensor assembly as measured by a sensor receiver disposed at the first sensor assembly; and   determining a starting alignment position of the first sensor assembly to be a first cross direction position where a difference between the sensor value at the first cross direction position and a corresponding sensor value at one or more adjacent cross direction positions is a minimum.   
     
     
         2 . The method of  claim 1 , wherein each sensor value comprises a sensor reading or a magnitude of a sensor voltage signal. 
     
     
         3 . The method of  claim 1 , wherein:
 the sensor source comprises a source element configured to generate an emission; and   the sensor receiver comprises a receiving element configured to measure the emission.   
     
     
         4 . The method of  claim 3 , wherein:
 the source element is configured to emit at least one of: nuclear radiation, infrared light, visible light, and a magnetic field; and   the receiving element is configured to measure the at least one of: nuclear radiation, infrared light, visible light, and a magnetic field.   
     
     
         5 . The method of  claim 1 , further comprising:
 correlating the sensor values and the corresponding cross direction positions to determine a sensor value versus position profile curve.   
     
     
         6 . The method of  claim 5 , wherein the first cross direction position coincides with a zero slope or minimum slope of the profile curve. 
     
     
         7 . The method of  claim 1 , wherein determining the sensor value for each cross direction position comprises activating the sensor source and measuring a received signal at the sensor receiver. 
     
     
         8 . The method of  claim 1 , wherein the cross direction positions span a range covering opposite sides of an estimated position of a center line of the sensor source. 
     
     
         9 . The method of  claim 8 , wherein the cross direction positions are evenly spaced. 
     
     
         10 . The method of  claim 1 , wherein the method is performed off-web during a maintenance period. 
     
     
         11 . An apparatus comprising:
 a first sensor assembly configured to move in a cross direction relative to a web of material, the first sensor assembly comprising:
 a sensor receiver configured to receive and measure emissions from a sensor source disposed at a second sensor assembly; and 
 at least one controller configured to:
 control a motor configured to move the first sensor assembly to a plurality of cross direction positions relative to the second sensor assembly; 
 determine, for each of the plurality of cross direction positions, a sensor value associated with the sensor source as measured by the sensor receiver; and 
 determine a starting alignment position of the first sensor assembly to be a first cross direction position where a difference between the sensor value at the first cross direction position and a corresponding sensor value at one or more adjacent cross direction positions is a minimum. 
 
   
     
     
         12 . The apparatus of  claim 11 , wherein each sensor value comprises a sensor reading or a magnitude of a sensor voltage signal. 
     
     
         13 . The apparatus of  claim 11 , wherein:
 the sensor source comprises a source element configured to generate the emissions; and   the sensor receiver comprises a receiving element configured to measure the emissions.   
     
     
         14 . The apparatus of  claim 13 , wherein:
 the source element is configured to emit at least one of: nuclear radiation, infrared light, visible light, and a magnetic field; and   the receiving element is configured to measure the at least one of: nuclear radiation, infrared light, visible light, and a magnetic field.   
     
     
         15 . The apparatus of  claim 11 , wherein the controller is further configured to correlate the sensor values and the corresponding cross direction positions to determine a sensor value versus position profile curve. 
     
     
         16 . The apparatus of  claim 15 , wherein the first cross direction position coincides with a zero slope or minimum slope of the profile curve. 
     
     
         17 . The apparatus of  claim 11 , wherein the cross direction positions span a range covering opposite sides of an estimated position of a center line of the sensor source. 
     
     
         18 . The apparatus of  claim 17 , wherein the cross direction positions are evenly spaced. 
     
     
         19 . A system comprising:
 a first sensor assembly and a second sensor assembly, the first sensor assembly configured to be disposed on a first side of a web of material and to move in a cross direction relative to the web, the second sensor head configured to be disposed on a second side of the web opposite the first side and to move in the cross direction;   the first sensor assembly further configured to:
 move to a plurality of cross direction positions relative to the second sensor assembly; 
 for each of the plurality of cross direction positions, determine a sensor value associated with a sensor source disposed at the second sensor assembly as measured by a sensor receiver disposed at the first sensor assembly; and 
 determine a starting alignment position of the first sensor assembly to be a first cross direction position where a difference between the sensor value at the first cross direction position and a corresponding sensor value at one or more adjacent cross direction positions is a minimum. 
   
     
     
         20 . A non-transitory computer readable medium embodying a computer program, the computer program comprising computer readable program code for:
 moving a first sensor assembly to a plurality of cross direction positions relative to a second sensor assembly, the first and second sensor assemblies configured to move in the cross direction relative to a web of material;   for each of the plurality of cross direction positions, determining a sensor value associated with a sensor source disposed at the second sensor assembly as measured by a sensor receiver disposed at the first sensor assembly; and   determining a starting alignment position of the first sensor assembly to be a first cross direction position where a difference between the sensor value at the first cross direction position and a corresponding sensor value at one or more adjacent cross direction positions is a minimum.